Hydraulic pump



April 20, 1948. BOOTH 2,440,072

HYDRAULIC PUMP I 7 Filed Feb. 24, 1945 l 22 JW ATIORNEY Patented Apr. 20, l 948 HYDRAULIC PUMP Douglas Gerhard Booth, Ilford, England, assignor to The Plessey- Comp land, a British comp Application February 24, In Great Britain l Claims. 1

This invention relates to improvements in hydraulic double acting pumps which operate over a Wide range of high pressures more especially, but not exclusively, to the kind which are operated manually.

Hitherto, in pumps of the kind referred to, the capacity is comparatively small in order to obtain a reasonable working effort on the operating handle or the like, by reason of the fact, that as the pressure increases there is a corresponding increase in the operating effort, consequently, a larger volume cannot be pumped at a lower-pressure. If a large capacity is provided for, although being suitable for low pressure output, the efiort on the operating handle or the like would become excessive if required to work at high pressure.

The primary object of this invention is to provide a hydraulic pump in which the operating effort remains approximately uniform irrespective of the output pressure.

' The invention will be described by way of example with reference to the accompanying diagrammatic drawing.

According to the invention, a spring loaded bypass valve is arranged in a by-pass which communicates with the respective ends of the double acting pump cylinder, said valve is acted upon by the delivery pressure existing in the delivery line or high pressure side, and the pressure at which the by-pass valves open, is determined by the force exerted by the spring, whereby the volume displaced by the pump becomes smaller when the pressure reaches a predetermined value, thus preventing a maximum working effort being exceeded. This maximum effort corresponding with the pressure at which the by-pass valve opens and is set by means of the spring.

A feature of the invention, is that it can be applied to a double acting pump having two or more pump cylinders in which a separate spring loaded by-pass valve arranged in a by-pass is operatively connected to each individual double acting pump, and the tension of the springs provided in the by-pass valves may be so predetermined, that as the pressure of the pump increases the by-pass valves are opened in succession.

Referring to the drawing which shows diagrammatically a simple hand operated two cylinder double acting pump.

The pump body I is provided with two parallel pump cylinders 2, 3, each containing a piston 4, 5, which reciprocate in opposite directions by having their piston rods 6, 1, formed with a toothed rack 8, 9, which are in constant engagement any Limited, Ilford, Engany 1945, Serial No; 579,658 March 3, 1944 v the conduits l8, 2|

with a pinion ID at diametrically opposite positions. Said pinion Ill is fixed to a shaft II which in turn is rotatably mounted in the pump body I, and a handle I2 is keyed to said shaft H for manually operating the pump.

The pump body I has a common inlet l3 which communicates by way of conduits l4, IS, with the pump cylinders 2, 3. Spring loaded inlet valves l6, It are arranged in the conduit M at the respective ends of the pump cylinder 2 and spring loaded discharge valves ll, l'l are provided in conduit 8 at each end of the pump cylinder. Spring loaded inlet valves l9, l9 are arranged in conduit [5 at oppositeends of the other pump cylinder 3 and spring loaded discharge valves 20, 20 are provided in conduit 2| at each end of said pump cylinder 3. These said inlet valves Hi, It and I9, l9 and discharge valves IT, I! and 20, 20 are arranged in the usual manner for the delivery of fluid by way of to a common outlet port 22.

A separate by-pass 23 communicates with the discharge outlets of the pump cylinder 2 and another by-pass 24 communicates with the discharge outlets from the pump cylinder 3.

A by-pass valve 25, 25'- is contained in each by-pass 23, 24 and so arranged that the valve stems 25 of valves 25, 25 extending from one face of the valve terminates in the respective delivery conduits l8, 2| of the high pressure side of the pump. The stems 25 extending from the opposite face of the valves 25, 25 each terminate into a disc shaped head 25 chamber 26, 26 which communicate with the low pressure side or inlet [3 of the pump by way of conduits 21, 2! connected to conduits I 4, l4. Each said by-pass valve 25, 25 is spring loaded by means of a helical spring 25 contained inthe low pressure chambers 26, 26 which act upon the heads 25 of the respective valve stems 25 in such a manner, that the valves 25, i5 remain closed at normalpressure. These two springs 25 are of a different tension, so that, as the pressure increases the valve fitted with the weaker spring is opened first.

In operation the effort applied to the handle 12 forces liquid from the low pressure side I3 to the high pressure side 22 in the usual manner. As the pressure increases a point is reached at which the lever effort reaches a maximum in the delivery line.

The areas of the valve stems 25 are arranged in conjunction with the tension of the springs, so that, as the pressure reaches a. predetermined maximum which corresponds to the maximum lever eiiort the by-pass valve fitted with the weaker spring, for example, say valve 25, opens thereby reducing the capacity of its companion pump by reason that fluid is allowed to flow through said valve to opposite of the pump cylinder 2, thus the lever effort is reduced. As the pressure increases in the high pressure side the second by-pass valve 25* is forced ofi its seating when reaching a predetermined maximum when a similar operation takes place with the second pump as hereinbefore described with reference to by-pass valve 25 when fluid is free to flow past the valve 25 by way of conduit 24 to the respective ends of the pump cylinder 3.

By this arrangement the lever effort does not at any time exceed a predetermined force, thus the variation of the effort applied to the lever is comparatively small throughout the whole time 7 of pumping, by reason that the volume displaced by the pump is reduced in proportion to the increased pressure.

I claim:

1. A pump comprising in combination a pump body containing at least two pump cylinders, .conduits for-communicating respective ends of the pump cylinders with the supply and discharge sides of the pump and a by-pass communicating with the ends of each individual pump cylinder and a passage leading to the discharge conduits, inlet and discharge valves closing the inlet and discharge passages leading to and from the respective ends of the pump cylinder, common actuating means operatively connected to said pistons, and a separate spring loaded valve provided with a stem closing the passage in the by-pass between the ends of each cylinder and the stem of each said spring loaded valve closing the passages between the discharge conduit and by-pass conduit in said valve body.

2. A pump according to claim 1 including a piston and piston rod in each pump cylinder in which the efiect of working area on said piston and piston rod and the loading of each spring loaded valve closing the passages in the by-pass is determined by the requisite reduction of capacity when each said spring loaded valve is to QP 3. A pump according to claim 1 including at least one additional cylinder in the pump body.

4. A pump according to claim 1 including unequal loading of the spring valves closing the passagesin the by-pass.

5. A pump according to claim 1 including loading chambers in said pump body which communica'te with the supply side of the pump and a helical spring arranged in each loading chamber for acting upon the valve closing the by -pass between respective ends of each pump "cylinder. DOUGLAS GERHARD BOOTH.

REFERENCES CITED The following references are of record in the illeof this patent:

UNITED STATES PATENTS Number Name Date 685,704 Wilkinson Oct. 29; 1901 725,707 Hoffman Apr. 21, 1903 1,170,873 Brown Feb. 8, 1916 1,607,531 Haight Nov. 16, 192.6 2,247,261 Towler et a1 June 24', 1941 

